The MEALS!!! Definitely get a digital scale, one that reads in grams. I like this one
http://www.amazon.com/gp/product/B00FJFJDGS/ref=oh_details_o04_s00_i00?ie=UTF8&psc=1 and use it to weigh your snake. Best way is to get a big enough container for the snake, put it on the scale (without the snake) and turn it on. It will read 0g, that is called the "tare" rate because you don't want to add that to what you put in it to weigh. Put the snake in and it is a quick read, write down her weight.
I encourage everyone to keep a diary on their snakes, I always weigh mine right before their dinner, I play with them for a bit while inspecting them from every side. I note in the notebook (I am a writer, I use the olde-timey Composition books but there are computer programs that you can use too) and record the date, weight, what it ate (or didn't), when in blue, when they shed, and anything else unusual.
Here is a good link for what to feed a snake of your size, I have one girl about your size who is 400g, and a boy who is about 6" longer who is 850g. They really do grow at different rates so this is a good guide.
http://www.medusa-corns.webs.com/feedingchart.htm
You will also want a bigger tank, 20L is the minimum I would get, but anything longer with a bigger footprint is ideal.
Tell us more about this girl!